This disclosure relates generally to flyback converter-based power converters that are capable of providing multiple output voltage levels in an efficient manner. Other embodiments are also described herein.
Alternating current (AC) power is typically supplied from wall outlets and is sometimes referred to as line power. Electronic devices often include circuitry that runs from direct current (DC) power. AC to DC power converter circuitry can be used to convert AC power to DC power. The DC power from such converter circuitry may be used to power an electronic device. The DC power may also be used to charge a battery in an electronic device.
AC to DC power converters often include transformers. A transformer in an AC to DC power converter may have primary and secondary windings. A pulse width modulation (PWM) circuit on the primary side of a transformer may generate pulses of current that pass through the primary winding of the transformer. On the secondary side of the transformer, a diode may be used to rectify the output of the secondary winding.
Some AC to DC power converter circuits use synchronous rectifier (SR) output stages. SR output stages may include a metal-oxide-semiconductor field-effect transistor (MOSFET). The MOSFET is driven so as to rectify the output waveform from the transformer in the same way that the diode is used in other power converter designs, while avoiding high diode voltage drops when conducting current (e.g., ˜0.7V).
Certain power converter designs may have potential drawbacks. One drawback is that different electronic devices may have different voltage requirements, and a single power converter may not be able to satisfy all of the requirements of all the different devices. For instance, a laptop computer may require a higher amount of power during operation than the amount of power required by a mobile phone, e.g., a laptop could require two to three times the amount of power (or more) of a mobile phone. The power converter used to operate the mobile phone may not provide a sufficient amount of voltage to operate the laptop and the power converter used to operate the laptop may provide too much voltage and overpower the mobile phone.
To address some of these drawbacks, some power converters may employ a “tapped winding” configuration. A tapped winding transformer refers to a transformer where the turns-ratio of the transformer may be adjusted to produce high and low output voltage ranges, as desired. However, “tapped winding” configurations can result in an overly complex circuit design, e.g., when two or more voltage output levels are required. Thus, what is needed is an intelligent flyback converter design to support multiple output voltages, e.g., by using a transformer with a tapped secondary winding and one or more switching devices to control the duty cycle and perform synchronous rectification, that is able to regulate output power at two or more voltage output levels using a minimally-complex circuit design that is optimized for each of the two or more voltage output levels.